Heretofore mechanical refrigeration units and spray systems have been employed for cooling or freezing food products.
Mechanical refrigeration systems generally employ Freon 22 or ammonia as a refrigerant and employ brine or air as intermediate coolant.
Spray systems generally spray vapor of cryogenic liquid, such as nitrogen or carbon dioxide, through nozzles into a compartment through which food is conveyed. Spray systems have ceratin advantages over mechanical refrigeration units heretofore devised because of faster freezing and consequently less shrinkage, simplicity of operation, ease of maintenance and relatively low initial installation cost. However, a primary disadvantage of spray systems as compared to mechanical refrigeration units involves higher operating cost because the cooling capacity of the vapor has not been efficiently utilized. Further, meats exposed to a nitrogen enriched atmosphere often absorb the nitrogen resulting in discoloration of the meat.